The goal of this Clinical Research Core Facility is to identify early immunologic and virologic markers of increased risk of developing DHF (Project 1). This core will measure plasma markers of immune activation in patients enrolled in Project 1 studies: cytokine levels, e.g. IL-Ibeta, tnf-ALPHA, il-2, il-6; levels of products of T cell activation, e.g. soluble CD8 (sCD8), soluble CD4 (sCD4); and levels of mediators of shock and plasma leakage, e.g. platelet activating factor (PAF), and complement components. The core will assess cellular immune responses in selected patients enrolled in Project 1: expression of T lymphocyte markers e.g. IL-2 receptors, HLA DR; monocyte/macrophage activation e.g. upregulation of Fc receptors; and the level of dengue-specific cytotoxic T lymphocyte activity during acute infections. (D and DHF). This core will quantitate neutralizing and enhancing antibodies to dengue virus in a human monocyte assay. The core will also perform diagnostic and quantitative virologic studies for Project 1, e.g. dengue virus isolation in mosquitoes, measure dengue antibody responses and detect dengue antigens by immunocytochemical techniques in PBMC of acutely ill patients. The core will analyze correlations between Class I and Class II histocompatibility (HLA) types of patients enrolled in Project 1 with D vs. DHF. The core will also assess the long term neutralizing and enhancing antibodies and T cell memory in patients in Project 1 with D or DHF. These results will characterize HLA-associated immune responses to dengue, and assess long-term beneficial (neutralizing) and detrimental (enhancing) antibodies which are important for vaccine development. This facility in Thailand will process, cryopreserve and ship patient samples (plasma and PBMC) from Project #1 for molecular immunologic studies in Project 2 (UMMC) and molecular characterization of virus strains in Project 3 (YARU).